Microstructure and magnetic properties of soft magnetic composites based on silicon resin coated Co40Fe22Ta8B30 glassy powders

In this paper, new Co40Fe22Ta8B30 bulk glassy and composite cores were prepared by powder metallurgy method. The CO40Fe22Ta8B30 glassy powder precursor was obtained by controlled ball milling of the melt-spun amorphous ribbons. As-milled metallic powders, as well as metallic powder particles coated by a silicon resin with very high thermal stability, were hot pressed at temperatures above the glass transition temperature of the metallic alloy powders. Therefore, monolithic glassy samples, as well as composite cores with high relative density, were obtained. The X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses confirmed that no devitrification was happened upon consolidation. The elemental mapping analysis using the energy dispersive X-ray method (EDX) indicated that the glassy powders were electrically insulated by silicone resin after hot pressing. The monolithic glassy cores showed a high relative density of 99% and wide supercooled liquid region of 74 K before crystallization, which is the same as that of the as-cast and ball milled CO40Fe22Ta8B30 amorphous ribbons. In addition to high thermal stability, the monolithic glassy cores exhibited good soft magnetic properties, e.g. high initial permeability of 1500, low coercivity of 13 A/m and magnetization of 43 Am-2/kg at f = 100 Hz. Addition of the silicon resin was effective to enhance the electrical resistivity and frequency stability of the initial permeability. The relaxation frequency of compacted cores increased from 1.1 kHz for monolithic glassy samples to 36 kHz upon addition of 2.5 wt.% silicon resin. In addition, Co40Fe22Ta8B30 glassy composites showed high initial permeability of 575 up to 14 kHz and low DC coercivity of 30 A/m. (c) 2013 Elsevier Ltd. All rights reserved.